XLIB Programming Manual, Rel. 5, Third Edition

5.4 Controlling Coloring and Patterning

The first stage of the drawing process (pixel selection) results in a bitmap with bits set to one indicating the pixels to be drawn. However, a window on a color display (or a pixmap to be copied to a color display) must have multiple bits per pixel to represent colors. The second stage of the drawing process colors the pixels.

There are four ways of coloring the pixels, controlled by the fill_style member of the GC. One of them uses a single color, and the other three apply patterns in different ways. You can pattern anything you can draw, including text, although lines of width 0 are not patterned.

We will begin by discussing the simple case, drawing with only the foreground color using fill_style of FillSolid. Then, to understand the effect of the patterning values for the fill_style, we must digress into a short description of tiles and stipples, followed by a discussion of the three styles of patterning.

5.4.1 Drawing in Foreground Only

Basic drawing is done using the foreground member of the GC. The foreground specifies the pixel value to be applied to the pixels selected by the graphics primitive, when the fill_style is FillSolid.^[13] The uses of the background color are restricted and are described in 5.4.5 Drawing in Foreground and Background. You can set the foreground with XSetForeground().

Figure 5-10 shows the use of the foreground pixel value when drawing a character with XDrawString(). We will contrast this later with a string drawn ...